Coolant problems and sluge in motor. Any ideals? on 2002 Pontiac Grand Prix

I bought this car new in 2002. It has 154,000 miles on it. I have always ran 10-30 synthetic valoline oil in it since day one and have changed oil and filter every 3000 to 5000 miles and still have sluge in the motor. When i take the oil cap off it has yellow gunk stuff up around cap. What could possible be going on with this motor.
Has far as the coolant problems, the motor does not over heat but, wants to use coolant every 2 or 3 weeks of normal driving. It wants to spray coolant all over the belt and battery on the right side of motor and notice some steam around top radiator and i have black soft flakes in the coolant. Also on the left side motor i ntoice water on top transmission. I have replaced water pump and heater valve tubes and flushed out coolant and replaced with new coolant. Sorry for length message. Thanks!

i just replaced the plumings top of motor 1 year 1/2 ago. I do have a little antifreeze up on top of motor. Do you think the plum could be bad again or just needs to be retighten. Doesn't those plumings need to be torque to a certain spec? Also do you have any ideal what the sluge could be all from and gunk up around the oil cap?

DO NOT DRIVE THIS CAR ANYMORE! If you do you will be putting an engine it.
You need to verify where the coolant leak is. That is done with a pressure tester.
Sluge is not based on the oil cap deposits. Keep using synthetic lubricant. I would use 5-30 instead of 10-30.

What do u mean do not drive no more? The engine does not over heat anything like that. Just using coolant little and leaking up on top of the motor up around the pluming. What do you mean about the sluge is not based on the oil cap deposits? I'm beganning think the oil isn't no good i'm using. I'm the first owner and have used this valoline synthetic oil sincee first oil change. What can i do to clean out the sluge out of engine? Thanks

Coolant does not evaporate. You have a coolant leak. If you wait till you see the temp gage register hot than it's to late. In my opinion the lubricant that you are using is not my choice. Use Amsoil or Mobil 1 FULL SYNTHETIC.

You're talkig about a Pontiac Grand Prix - is that correct? They require Dex-Cool Coolant and it comes pre-mixed. Sluge can come from using wrong coolant, stop leak,etc because rust will build up. Know problem with front gasket of the intake manifold in these cars. Beats me why the cars weren't recalled.